Clean git repo on Heroku

The situation is as follows:

We have some project which persists on Github, and deploy it to Heroku, which has its own mini-Git. Some changes were applied directly to Heroku (cloned repository from Heroku, made changes and pushed). In a meanwhile the master branch on Github has gained also some changes.

Now when I want to push the main repository to Heroku, pushing fails because commits on Heroku are out of sync with local commits.

I do not want to merge with changes on Heroku - I just want them to vanish.

Is there some way to clean git repository on Heroku to push then my local repo from the very beginning?

I do not want to destroy application and recreate it again because it has some paid services and I am just an collaborator.